Device for accurately positioning X-ray filters in the beam path



Aprl] 26, 1966 J. VAN DE GEUN 3,248,547

DEVICE FOR ACCURATELY POSITIONING X-RAY FILTERS IN THE BEAM PATH Filed Oct. 21, 1963 INVENTOR.

JOHAIVNES VAN DE GE/JN ATTORNEY United States Patent DEVICE FOR ACCURATELY POSITIONING X-RAY FILTERS IN THE BEAM PATH Johannes van de Geijn, The Hague, Netherlands, assignor to Picker X-Ray Corporation, Waite Manufacturing Division, Inc., Cleveland, Ohio, a corporation of Ohio Filed Oct. 21, 1963, Ser. No. 317,487

6 Claims... (Cl. 250--86) This invention relates to X-ray and related apparatus and more specifically to a novel and improved filtering mechanism for use in conjunction with a penetrating ray source.

In medical radiation treatments, it is frequently desirable to change characteristics and distribution of a field penetrating radiation. As one example, in radiological studies, it is desirable to use a wedge shaped filter in radiographic studies of pregnant women where it is desired to simultaneously obtain an X-ray of the placenta and of the backbone. The backbone is relatively opaque to X-radiation and requires a high energy level while the placenta is relatively transparent to the radiation requiring a relatively low level. Without alteration of the field of radiant energy through the use of a wedge type filter, it would be impossible to obtain, on a single radiographic film, an X-ray of both the placenta and the backbone.

Similarly, in therapy treatments, utilizing apparatus such as that described in United States Patent No. 2,959,- 680, issued November 8, 1960, .to Donald T. Green, under the title, Adjustable Collimator for Radiation Therapy, it is desirable to adjust the distribution of the penetrating radiation used in the therapy treatment. The purpose of the wedge filter in the therapy treatment is to control the field distribution so as to come as close as possible to the idea of treating only diseased tissue while not effecting surrounding normal tissue.

The use of wedge filters to control the distribution of an energy field, for the reasons set out above and for other purposes, is well known. In the past, these systems have used either of two main methods. These methods are:

(1) A separate wedge filter for every field size; and,

(2) A single wedge for all fields with the wedge large enough to accommodate the largest field size of the associated apparatus.

The first of these has the disadvantage of requiring substitution of a different filter whenever a field size is changed. The second has the disadvantage of absorbing unnecessary amounts of radiation in all but the largest field size opening because the beam in smaller field sizes passes through an unnecessarily thick portion of thefilter.

The present invention provides the advantages of both prior mechanisms, without their disadvantages, in a single device. able so as to obtain the appropriate amount of filtration for all field sizes.

In radiation treatment planning for individual patients, an important type of tool is formed by the so-called isodose-charts, two dimensional dose distributions visualized by lines connecting points with equal dose.

With both modified and wedged beams, these isodose charts are usually measured in suitable so-called phantoms, the beam at right angles to the (fiat) surface.

In clinical practice one is often confronted with situations in which the beam enters at an angle of either about 30 degrees or 45 degrees with the normal to the surface. It is of great importance to maintain the use of the standard isodose charts in these conditions. To that end, two additional wedge type filters (compensators) were developed, one for dealing with an angle of incidence of about 30 degrees, the other for an angle of about 45 degrees.

The conditions of oblique incidence occur for both un- That is, it provides a single filter which is adjust- 3,248,547 Patented Apr. 26, 1966 modified and modified beams. Therefore, it is necessary to be able to use the beam modifying wedge filter and one I of the compensators simultaneously.

To obtain this objective a construction is provided in which a pair of filters can be positioned in superposed relationship. The positioning of both is adjustable so as to obtain the previously described benefit of optimal functioning of the wedge filter and one of the compensators simultaneously, with any field size.

With this invention a wedge filter is mounted on a support plate to form a filter subassembly. The subassembly is rectilinearly movable in suitable tracks to position the filter across the path of the penetrating ray beam. The subassembly has a light slit paralleling and immediately adjacent the thinnest edge of the filter. A light source is provided and adapted to emit a light beam through a collimator corresponding to the penetrating ray beam.

When the device is in use, the filter is shifted rectilinearly until the light beam, which passes through the slit, just begins to disappear. When the light beam commences to disappear, the edge of the filter is at the edge of the light beam and, therefore, the edge of the radiation field. The wedge filter is appropriately positioned for a given field when its thin edge is at the edge of the field.

Where two filters are used, the first filter is first positioned with its edge at the edge of the field. The second filter is then placed in tracks paralleling the tracks for the first filter and spaced below them. The second filter is moved until the slit of light passing through the first filter subassembly slit passes through a similar second filter slit. At this time, the edge of the second filter is at the edge of the penetrating radiation beam and the filtering mechanism is positioned for the study to be conducted.

Accordingly, the object of this invention is to provide a novel and improved wedge filter structure.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims taken in conjunction with the accompanying drawing in which:

FIGURE 1 is a schematic fragmentary side elevational view of a radiant energy source and collimator showing the structure of this invention in cross section as seen from the plane indicated by the line 11 of FIGURE 2;

FIGURE 2 is a sectional view of the device of this invention as seen from the plane indicated by the line 22 of FIGURE 1;

FIGURE 3 is a schematic view showing the positioning of the wedge filters of this invention; and,

FIGURE 4 is an enlarged fragmentary view showing a clamping mechanism for the wedge filters of this invention.

Referring now to the drawings and to FIGURE 1 in particular, a housing or head is shown generally at 10.

The head 10 encases a source of penetrating radiation and is equipped with a collimator such as that shown in phantom at 11. The collimator 11 may be of the type described and claimed in the above-referenced patent. A wedge filter assembly is shown generally at 12 and in solid lines in the drawings. The assembly 12 includes a supporting plate 13 which is positioned immediately below the collimator 11. The support plate 13 is secured to the head 10 by suitable means such as four studs 14, only one of which is visible in FIGURE 1. Knurled nuts 15 are connected to each of the studs 14 to clamp the support plate 13 against a series of spacers 16. The support plate 13 has a central square beam aperture 17 which is aligned with a beam emitting passage in the collimator 11.

A pair of filter support guides or tracks 18 are secured to the underside of the support plate 13. The tracks 18 are parallel and disposed on opposite sides of the beam opening 17. The tracks 18 are symmetrically disposed 3 about the center or axis of a beam. The details of one of the tracks 18 are shown in FIGURE 4.

Each track 18 includes a supporting generally L- shaped track block 19 which is suitably secured to the plate 13. An upper track guide 20 is secured to the supporting plate 13 in spaced relationship with a horizontally disposed track surface 21 on the track block 19. A longitudinally disposed guide space is, then, defined by the track surface 21 on the guide block 19 and the track guide 20.

A plate-like filter slide 23 is carried by the tracks 18. The filter slide 23 has a beam aperture 24 which is square and may be of a size corresponding to the beam aperture 17 in the support plate 13. A wedge shaped filter 25 substantially covers and is disposed below the beam aperture 24. The filter 25 may be secured to the filter slide 23 by a suitable filter cover 26.

The filter slide 23 has a downwardly projecting tab handle 27 to facilitate rectilinear adjustment of the filter slide 23 and the tracks 18. The filter slide 23 and filter 25 together define a slit at 30 which is aligned with a filter cover slit. The slits 30 are for purposes which will be described below.

A clamping mechanism for maintaining the filter slide 23 in an adjusted position is shown best in FIGURE 4. The clamping mechanism consists of an L-shaped clamp member 31 which abuts the lower face of the filter slide 23. The L-shaped clamp member 31 has an aperture 32 through which a clamp bolt 33 extends. The clamp bolt 33 is threaded into the guide bar 19. Tightening of the clamp bolt 33 clamps the clamp member against the filter slide 23 holding it in an adjusted position.

For many applications the previously described mechanism is ample. For others, a second filter may be desirable in which case a second support plate 35 corresponding to support plate 13 is provided, The second support plate is secured to the support plate 13 by suitable studs and spacers 36, 37. A pair of filter tracks 38, only one of which is shown, corresponding to the tracks 18, are secured to the second support plate 35. A second filter plate 43 is provided which includes a tab handle 47. The second filter plate is rectilinearly movable in the filter tracks 38. The construction of the filter tracks 38 and of the second filter slide 43 are substantially identical to the previously described filter slide and tracks.

The second filter slide 43 has a beam aperture 44 and a wedge filter 45 corresponding to the aperture and filter 24, 25. It also has a clamp nut 53 corresponding to the clamp nut 33 and acting against a second clamp member identical to the clamp member 31 but not shown.

The second filter slide 43 is equipped with a light slit 60 for a purpose which will be described presently.

Referring now to FIGURE 3, a penetrating ray energy source is shown generally at 65. A light energy source is shown generally at 66 and a mirror is shown at 67. The light source acts against the mirror to provide a light beam passing through an aperture in collimator 11 to correspond in cross-sectional area to the beam of ray energy emitted by the source 65.

When the device is used, the second filter slide 43 will be removed and the first filter slide 23 moved reciprocally to an adjusted position. The appropriate locating of the filter 25 is accomplished by sliding the filter slide 23 back and forth until the slit of light passing through the slit 30 just begins to disappear. When the light slit begins todisappear, the slit will be at the edge of the beam emitted by the light source 66 and reflected by the mirror 67 and, therefore, the thin edge of the wedge filter 25 will beat the edge of the beam. Once the first filter 25 is positioned, the second filter slide 43 may be placed in its tracks 38 and slid back and forth until the thin slit of light passing through the slit 30 appears and passes through the slit 60. At this time the thin edge of the wedge filter 45 will be aligned with the edge of the radiant energy beam and the device is ready for use.

As suggested above, with some applications only the filter 25 is required and, of course, the described steps.

of positioning the filter 45 is not then required.

While the device has been described with detail, it is believed that it essentially comprises, in combination with an energy source, a light source, a wedge filter, and a filter support mechanism including a slit along-the thin edge of the wedge with the filter being movable transversely across the beam until light passed throughthe slit commences to disappear, thereby locating the filter in the appropriate position for a selected beam size.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without department from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. Radiant energy apparatus comprising in combination:

(a) a penetrating radiation source for emitting a penetrating beam;

(b) a light energy source for emitting a light beam corresponding to the penetrating beam;

(c) a guide means secured to said penetrating radiation source and positioned to provide guiding transverse to said beams; and

(d) a filter subassembly including a wedge filter, the subassembly being movably supported in said guide means for movement transverse to the beams. to position the filter across the beams, said subassembly including a light transmitting slit for locating the edge of said beam of light, said slit being adjacent one edge of said filter.

2. In combination:

(a) a head including a source of penetrating radiation;

(b) a collimator secured to the head;

(0) a light source to emit a light beam through the collimator corresponding in cross-sectionalarea to a beam of penetrating radiation emitted by said penetrating radiation source;

(d) a pair of parallel tracks secured to the radiation source and disposed symmetrically on opposite sides of said light beam;

(e) a filter slide rectilinearly movable in said tracks and including a beam passage;

(f) a filter of varying thickness and including a thin edge, the filter being secured to the filter slide and substantially covering said beam passage; and,

(g) said filter slide and filter forming a subassembly including a light transmitting slit adjacent and paralleling the thin edge of said filter whereby to permit an operator to locate the edge of said light beam and position a selected portion of said subassembly at said edge.

3. The device of claim 2 wherein a clamp means is carried by the track and engageable with said slide to lock the slide in an adjusted position.

4. The device of claim 2 wherein:

(a) a second set of tracks is positioned parallel to the first set with the first set between the second set and the collimator;

(b) a second filter slide is carried by the second se of tracks;

(0) said second filter slide is equipped with a beam aperture;

(d) a second wedge filter substantially covers the second slide aperture; and,

(e) the second filter and slide define a second light transmitting slit paralleling and adjacent the thin edge of said second wedge filter.

5. Penetrating radiant energy apparatus comprising:

(a) a housing encasing a penetrating radiant energy source;

(b) a collimator for delineating a beam emitted by said penetrating source;

(c) a light source for emitting a beam of visible light through said collimator;

(d) a support plate secured to said housing and including a beam aperture surrounding the beams; (e) a pair of parallel tracks disposed transversely of the beams and secured to the plate symmetrically on opposite sides of the aperture;

(f) a filter slide reciprocally mounted in the tracks and including a beam aperture alignable with the plate aperture;

(g) a wedge shaped filter secured to the slide and substantially closing said slide aperture;

(h) said filter and slide comprising a subas'sembly defining a light transmitting slit paralleling and adjacent one edge of the filter; and,

(i) means to clamp the sub-assembly in an adjusted position.

6. Radiant energy apparatus comprising in combination:

(a) a penetrating radiation source for emitting a penetrating beam;

(b) a light energy source for emitting a light beam corresponding to the penetrating beam;

RALPH G. NILSON, Primary Examiner.

(c) first and second spaced guide means secured to said penetrating energy source, each positioned to provide guiding tracks transverse to said beams;

(d) first and second filter subassemblies positioned respectively in the first and second guide means; and,

(e) each filter subassembly including a Wedge filter, the subassembly being movable in said guide means for movement transverse to the beams to position the filter across the beams, each subassembly including a light transmitting slit for locating the edge of said beam of light, each of said slits being adjacent one edge of its filter.

References Cited by the Examiner UNITED STATES PATENTS 1,976,179 10/1934 Mannl 250 2,474,422 6/1949 Hollstein 250105 2,506,342 5/1950 Burke 25086 2,630,536 3/1953 Vladefi 250-86 2,894,144 7/1959 Barrett 250-105 FOREIGN PATENTS 1,145,277 3/ 1962 Germany.

79,741 9/ 1932 Switzerland. 

1. RADIANT ENERGY APPARATUS COMPRISING IN COMBINATION: (A) A PENETRATING RADIATION SOURCE FOR EMITTING A PENETRATING BEAM; (B) A LIGHT ENERGY SOURCE FOR EMITTING A LIGHT BEAM CORRESPONDING TO THE PENETRATING BEAM; (C) A GUIDE MEANS SECURED TO SAID PENETRATING RADIATION SOURCE AND POSITIONED TO PROVIDE GUIDING TRANSVERSE TO SAID BEAMS; AND (D) A FILTER SUBASSEMBLY INCLUDING A WEDGE FILTER, THE SUBASSEMBLY BEING MOVABLY SUPPORTED IN SAID GUIDE MEANS FOR MOVEMENT TRANSVERSE TO THE BEAMS TO POSITION THE FILTER ACROSS THE BEAMS, SAID SUBASSEMBLY INCLUDING A LIGHT TRANSMITTING SLIT FOR LOCATING THE EDGE OF SAID BEAM OF LIGHT, SAID SLIT BEING ADJACENT ONE EDGE OF SAID FILTER. 